<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <input type="text" placeholder="半径" id="a">
    <input type="text" placeholder="周长" id="b">
    <input type="text" placeholder="面积" id="c">
    
 <script>
      var r = prompt("请输入圆的半径");
                
        document.querySelector("#a").value = r;
     
       var lone = r;
       var p = 3.14;
       var l = (lone * 2 * p);
      document.querySelector("#b").value = l;
       var s = (p * lone )* (p * lone );
    document.querySelector("#c").value = s;

 </script>   			
   	

</body>
</html>